How to cook with, clean, and buy a microwave. Here, everything you didn't know you needed to know about your most used kitchen appliance.

Shopping for a new microwave? The Good Housekeeping Research Institute's Food Appliances director, Sharon Franke, answers the questions on your mind.

What should I consider before I start shopping for a microwave?

Size matters. Before you go shopping, determine how much kitchen space you're willing to give up for the microwave — and how you're planning to use the appliance. If you're feeding a family, go for a bigger oven (1.2 cubic feet or more) that can handle large dishes, like casseroles and lasagnas. Pressed for room on the countertop? Manufacturers are making models as small as .5 cubic feet that do a great job for just heating up soups or coffee.

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What should I look for in the store?

Look for must-have features that take the guesswork out of preparing meals, like automatic defrost and preprogrammed settings that warm up snacks. Another cool option: sensors that calculate cooking time based on the amount of steam the food emits.

See if your favorite dish fits on the turntable. If the dish is too wide to rotate, look for a feature that lets you shut off the turntable so it's stationary during cooking.

Find out if the machine is user-friendly. Look for large buttons and icons. Open and close the door a few times to see if you like the way it feels.

How much wattage do I need?

A 1,000-watt microwave will cook quickly and efficiently. Microwaves with 700 watts or less are slower and may not cook evenly. In general, the higher the wattage, the faster the cooking time.

Are there models that are best for families?

Absolutely. Look for ones with easy-to-read preprogrammed settings. They make preparing snacks like popcorn and soup a breeze. (Just be sure to show inexperienced family members how to safely use the machine. If a child is too young to use the range or electric appliances, she shouldn't use the microwave unsupervised.)

How often should I replace my model?

Microwaves typically have a life span of about 10 years. But if your unit is operating properly after that amount of time, you can continue to use it.

Are there reasons to replace my microwave if it still works well?

You'll want to replace or repair any unit with any defects in the door or in the seal around the door.

What are some innovations worth considering?

If your son or daughter is too young to use a microwave, be sure the oven has a child lockout feature. It's easy to use: Adults have to press a sequence of buttons (1234, for example) before being able to operate the appliance. Manufacturers have been coming out with space-saving multitasking microwaves that are intriguing. For example, some machines double as convection ovens. Others are equipped with a built-in coffee maker or toaster. There is even one with a rotisserie.

How do I keep my food from overheating and boiling over when microwaving?

Use a cover to prevent splatters. When you want to allow some steam to escape, use a paper towel or waxed paper. To hold in moisture, use plastic wrap or a lid designed for microwave cooking.

If your meal is prone to splattering — like cooked cereals and tomato sauce — use a bigger bowl. This gives the food more room to boil.

To prevent overheating, stir food once or twice during cooking.

Can I put aluminum foil in the microwave?

Aluminum foil isn't off-limits in the microwave. It generally isn't used because the foil deflects the microwaves away from the food. However, you can place a small, flat sheet directly on top of the food or in a corner to prevent overcooking. Make sure there are no crinkles — they can cause sparks.

How should I clean my microwave?

Before wiping down your appliance, spray an all-purpose cleaner onto a cloth. Never spray it directly into the oven. If cleaner gets sprayed into the vent holes in the oven, it can damage the internal parts. Be sure to clean the interior ceiling inside the microwave — it catches a lot of splattered food and liquid. Clean the turntable by hand washing or by placing it in the dishwasher.